Current white-light-emitting phosphor-conversion LEDs (pc-LEDs) utilize one or more phosphors to partially absorb blue light emissions from InGaN LEDs in order to convert some of the blue light into a yellow light. The combination of the remaining unabsorbed blue light and converted yellow light yields light which is perceived as white. Other phosphors may be used in addition to the yellow-emitting phosphor, for example a red-emitting phosphor, in order to increase color rendering index (CRI) or achieve a different color temperature (CCT). However, the yellow-emitting phosphor remains the core component in white pc-LEDs.
The normal yellow-emitting phosphor used in a pc-LED is a cerium-activated yttrium aluminum garnet, Y3Al5O12:Ce, phosphor (YAG:Ce). However, other phosphors include a cerium-activated terbium aluminum garnet (TAG:Ce) phosphor as described in U.S. Pat. No. 6,669,866 and silicate-based phosphors such as those described in U.S. Pat. Nos. 6,943,380, 6,809,347, 7,267,787, and 7,045,826.
An example of a YAG:Ce phosphor and its application in an LED are described in U.S. Pat. No. 5,998,925. Some composition modifications of YAG phosphors are also described in this patent, such as using Ga to replace Al or Gd to replace Y in the garnet. Generally, Ga substitution of Al shifts the emission peak to shorter wavelength and Gd substitution of Y shifts emission peak to longer wavelength.